1. FIELD OF THE INVENTION
This invention relates to a fiber optic switch of the moving fiber type.
2. DESCRIPTION OF THE PRIOR ART
Fiber optic switches are now commonly used in communication networks and laboratory installations, and at the present, only mechanically activated switches offer both low cost and good crosstalk performance. In general, mechanical or electromechanical fiber optic switches can be classified in two basic types, i.e., moving beam and moving fiber. Moving beam switches include optical collimating lenses which expand the beam of light from the fibers, and then by way of movement of prisms or mirrors, the expanded beam is redirected as required in the switching process. Moving fiber switches, on the other hand, involves the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of the beam of light from one fiber end to another under selected switching conditions.
The moving beam type switches have a somewhat relaxed tolerance of movement control because of the use of the expansion lenses, but this is at the expense of a large, more complex and costly assembly which generally requires a more powerful actuator to move prisms or mirrors between switching positions. In the moving beam switches, the actuators are usually of the electromagnetic type, i.e., relays or solenoids, and therefore require significant operating power. As an example, commercially available switches, such as that know as the NEC OD-8754 optical switch, which is a moving beam type and is a single pole, double throw, (SPDT), for multi-mode fiber, although using a magnetic latching mechanism to eliminate holding power, requires switching energy for its electro-magnet in the order of 10 millijoules. Without the use of a magnetic latching mechanism significant holding power, such as fractions of a watt, is required.
In a moving fiber type switch, actuator power requirements are significantly reduced because only the small mass of the fiber itself need be moved. On the other hand, the moving fiber switches have a stringent tolerance requirement for the amount and direction of movement, the amount typically being a small portion of the fiber core diameter. In any event, the requirement of a much lower force to move the fiber has resulted in attempts to produce a SPDT switch in which a piezo-electric actuator is used. An example of such a switch is shown in a publication "Mechanical Fiber Optic Switching using P.V.D.F. Bimorph" by T. Ebato et al, Elect. Lett., Vol. 16, #22, Pg 829-830. It is indicated in this publication that the disclosed switch achieves a low loss of 0.7 dB, but it is to be noted that this is with only a 60 .mu.m multi-mode fiber. The disclosed piezo-electric film actuator is very weak, resulting in slow switching and a fragile assemble. Moreover, the fiber registration scheme shown in the publication is not satisfactory for use in a single mode fiber arrangement. The light carrying core of a single mode fiber is typically 9 microns in diameter and therefore requires a more precise registration than is the case for a multi-mode fiber.
There are shown in two additional publications, namely "New Optical Switch Development", by H. Laor, 7th ECOC, Copenhagen 1981, P14-1, and "Performance Characteristics of a 16-Channel Optical Switch using Directable Light Beams", by H. Laor and N. Egozi, OFC'82 Phoenix, TUG 8, the use of a stronger piezo-electric actuator in the form of a bimorph cantilever as an element in a large switching array. However, the disclosed arrangement does not include a control or registration device of a nature which could be used in a single mode fiber.
As indicated above, moving fiber switches have a tolerance requirement which is critical, and in proposed switches, in which the movable fiber is moved into alignment with a stationary fiber, highly machined parts have been utilized to obtain alignment which is acceptable to avoid unacceptable loss of the transmitted signal. The cost of producing such parts and the practices which must be adopted in assembling the parts to form the switch add significantly to the cost of the product.